Ever heard of the 'No true scotsman' fallacy?
If not there is an explanation of it here:
No true Scotsman - Wikipedia
Ok, now you have unintentionally got me annoyed. It bugs me when people say this because;
a) It is not true for many terrorists who do follow their religion and would vehemently disagree with you that they are not following their religion.
b) It appears to imply that all the terrorists are non-religious, which I see as a kind of slur of the non religious to say that all the terrorists belong to us
In my opinion.